Projector

ABSTRACT

A projector that outputs a first picture and a second picture alternately, wherein a control section performs first control and second control, controls a discharge lamp driving section. In the first control and the second control, the absolute value of a drive current is relatively small in a first period and relatively large in a second period. In the first control, the energy provided to a first electrode in the second period is greater than the energy provided to the second electrode in the second period. In the second control, the energy provided to the second electrode in the second period is greater than the energy provided to the first electrode in the second period.

This is a Continuation application of application Ser. No. 13/306,218filed Nov. 29, 2011. The disclosure of the prior application is herebyincorporate by reference herein in its entirety.

BACKGROUND

1. Technical Field

The present invention relates to projectors.

2. Related Art

A projector using a discharge lamp such as a high-pressure mercury lampor a metal halide lamp has been put to practical use. As such aprojector, in JP-A-2003-102030, for example, a projector having a unitfor varying the intensity of a light source in accordance with a colorseparation unit or the like in synchronization with a picture signal isdisclosed. However, JP-A-2009-237302 describes that if the intensity ofthe light source is simply varied, an electrode of the discharge lampwill wear out significantly.

Moreover, in recent years, a projector that outputs a stereoscopicpicture by using a discharge lamp such as a high-pressure mercury lampor a metal halide lamp has been put to practical use.

One of the methods to output a stereoscopic picture is a method by whichswitching between a picture for the right eye and a picture for the lefteye is performed and the picture for the right eye and the picture forthe left eye are alternately output (for example, active shutter glassestechnology such as “XPAND beyond cinema” (a trademark of X6D Limited)).In this method, the right eye is made to view the picture for the righteye and the left eye is made to view the picture for the left eye byusing active shutter glasses etc. synchronized with a picture signal,whereby the picture is made to appear stereoscopically by using parallaxbetween what the right and left eyes see.

When a stereoscopic picture is projected by the method by which apicture for the right eye and a picture for the left eye are alternatelyoutput, the amount of light that enters the right eye and the left eyeis less than half of the amount of light that enters the right eye andthe left eye when an existing two-dimensional picture is projected.Moreover, when crosstalk by which the picture for the right eye entersthe left eye or the picture for the left eye enters the right eyeoccurs, the observer loses the sense of viewing the stereoscopicpicture. Therefore, it is necessary to provide a period in which bothactive shutters are closed. As a result, when a stereoscopic picture isprojected by the method by which a picture for the right eye and apicture for the left eye are alternately output, the picture appearsdarker than when an existing two-dimensional picture is projected. Tomake the picture appear bright, the drive power can be simply increased.However, this increases the power consumption of the projector oraccelerates the deterioration of peripheral parts associated with theincrease in drive power.

Moreover, if control to reduce the brightness of the discharge lamp in aperiod in which both active shutters are closed and increase thebrightness of the discharge lamp in a period in which one of the activeshutters is opened is performed to make the picture appear bright, thetemperature of the electrode of the discharge lamp is reduced in aperiod in which the brightness of the discharge lamp is reduced,resulting in insufficient fusibility of the tip of the electrode. Thismay cause deformation of the electrode. When the electrode is deformed,there is a possibility of, for example, the occurrence of flicker.Therefore, special consideration is needed to prevent deformation of theelectrode.

SUMMARY

An advantage of some aspects of the invention is to provide a projectorthat can project a picture in such a way that the picture appears brightwhile preventing deformation of an electrode.

An aspect of the invention is directed to a projector that outputs afirst picture and a second picture alternately while performingswitching between the first picture and the second picture with givenswitching timing, the projector including: a discharge lamp including afirst electrode and a second electrode; a discharge lamp driving sectionthat supplies, to the discharge lamp, a drive current that drives thedischarge lamp; and a control section that controls the discharge lampdriving section, wherein a period sandwiched between a time at whichswitching is performed and the next time at which switching is performedstarts with a first period and ends with a second period, the controlsection performs first control in a first control period which continuesat least for a period sandwiched between a time at which switching isperformed and the next time at which switching is performed and performssecond control in a second control period which continues at least for aperiod sandwiched between a time at which switching is performed and thenext time at which switching is performed, the second control perioddifferent from the first control period, in the first control and thesecond control, the control section controls the discharge lamp drivingsection so that the absolute value of the drive current becomesrelatively small in the first period and becomes relatively large in thesecond period, in the first control, in the first period, the controlsection controls the discharge lamp driving section so that thedischarge lamp driving section supplies an alternating current to thedischarge lamp as the drive current, and, in the second period, thecontrol section performs first control processing by which the controlsection controls the discharge lamp driving section so that thedischarge lamp driving section supplies, to the discharge lamp, thedrive current by which the energy provided to the first electrode in thesecond period becomes greater than the energy provided to the secondelectrode in the second period, and, in the second control, in the firstperiod, the control section controls the discharge lamp driving sectionso that the discharge lamp driving section supplies an alternatingcurrent to the discharge lamp as the drive current, and, in the secondperiod, the control section performs second control processing by whichthe control section controls the discharge lamp driving section so thatthe discharge lamp driving section supplies, to the discharge lamp, thedrive current by which the energy provided to the second electrode inthe second period becomes greater than the energy provided to the firstelectrode in the second period.

According to the aspect of the invention, since the energy provided tothe first electrode becomes greater in the first control processing andthe energy provided to the second electrode becomes greater in thesecond control processing, the fusibility of the electrode is increased.This makes it possible to prevent deformation of the electrode.

Moreover, according to the aspect of the invention, since the controlsection controls the discharge lamp driving section so that the absolutevalue of the drive current becomes relatively small in the first periodand becomes relatively large in the second period, it is possible torealize a projector that can project a picture in such a way that thepicture appears bright.

In the projector, the control section may perform the second control ina period which is at least part of a period sandwiched between the firstcontrol periods which are next to each other in terms of time.

As a result, it is possible to keep a heat load balance between thefirst electrode and the second electrode of the discharge lamp. Thismakes it possible to prevent only one of the electrodes of the dischargelamp from wearing out.

In the projector, the control section may perform third control in athird control period which continues at least for a period sandwichedbetween a time at which switching is performed and the next time atwhich switching is performed, the third control period different fromthe first control period and the second control period, and, in thethird control, the control section may control the discharge lampdriving section so that the absolute value of the drive current becomesrelatively small in the first period and becomes relatively large in thesecond period, the control section may control the discharge lampdriving section so that the discharge lamp driving section supplies, tothe discharge lamp, the drive current by which the difference betweenthe energy provided to the first electrode and the energy provided tothe second electrode in the second period is smaller than thedifferences in the first control and the second control, and the controlsection may perform at least one of the first control and the secondcontrol in a period sandwiched between the third control periods whichare next to each other in terms of time.

As a result, it is possible to prevent harmful effects such asblackening caused by too high fusibility of the electrode due to thefirst control and the second control.

The projector may include a state detecting section detecting adeteriorating state of the discharge lamp, and the control section mayshorten the third control period with the progress of the deterioratingstate.

The state detecting section may detect, as a value indicating the degreeof the deteriorating state, for example, a drive voltage of thedischarge lamp, a temporal change in the drive voltage of the dischargelamp, the amount of light of the discharge lamp, a temporal change inthe amount of light of the discharge lamp, accumulated lighting time ofthe discharge lamp, or the like.

When the deteriorating state progresses, the fusibility of the electrodeis reduced. Therefore, by shortening the third control period with theprogress of the deteriorating state, it is possible to increase thefusibility of the electrode and prevent deformation of the electrode.

The projector may include a state detecting section detecting adeteriorating state of the discharge lamp, and the control section maylengthen the first control period and the second control period with theprogress of the deteriorating state. When the deteriorating stateprogresses, the fusibility of the electrode is reduced. Therefore, bylengthening the first control period and the second control period withthe progress of the deteriorating state, it is possible to increase thefusibility of the electrode and prevent deformation of the electrode.

In the projector, in the first control processing, the control sectionmay control the discharge lamp driving section so that the dischargelamp driving section supplies, to the discharge lamp, a direct currentby which the first electrode becomes a positive electrode as the drivecurrent, and, in the second control processing, the control section maycontrol the discharge lamp driving section so that the discharge lampdriving section supplies, to the discharge lamp, a direct current bywhich the second electrode becomes a positive electrode as the drivecurrent.

As a result, it is possible to realize the first control processing andthe second control processing with simple control.

In the projector, in the first control processing, the control sectionmay control the discharge lamp driving section so that the dischargelamp driving section supplies, to the discharge lamp, an alternatingcurrent by which the time in which the first electrode is a positiveelectrode, the time in one period, is longer than the time in which thesecond electrode is a positive electrode as the drive current, and, inthe second control processing, the control section may control thedischarge lamp driving section so that the discharge lamp drivingsection supplies, to the discharge lamp, an alternating current by whichthe time in which the second electrode is a positive electrode, the timein one period, is longer than the time in which the first electrode is apositive electrode as the drive current.

As a result, it is possible to realize the first control processing andthe second control processing with simple control.

In the projector, in the first control processing, the control sectionmay control the discharge lamp driving section so as to include a periodin which the discharge lamp driving section supplies an alternatingcurrent as the drive current and a period in which the discharge lampdriving section supplies, to the discharge lamp, a direct current bywhich the first electrode becomes a positive electrode as the drivecurrent, and, in the second control processing, the control section maycontrol the discharge lamp driving section so as to include a period inwhich the discharge lamp driving section supplies an alternating currentas the drive current and a period in which the discharge lamp drivingsection supplies, to the discharge lamp, a direct current by which thesecond electrode becomes a positive electrode as the drive current.

As a result, it is possible to realize the first control processing andthe second control processing with simple control.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is an explanatory diagram showing an optical system of aprojector according to a first embodiment.

FIG. 2 is an explanatory diagram showing the configuration of a lightsource device.

FIG. 3 is a diagram showing an example of a circuit configuration of theprojector according to the first embodiment.

FIG. 4 is a diagram showing an example of a circuit configuration of adischarge lamp lighting device.

FIG. 5 is a diagram for explaining another configuration example of acontrol section.

FIGS. 6A to 6D are explanatory diagrams showing the relationship betweenthe polarity of a drive current which is supplied to a discharge lampand the temperature of an electrode.

FIG. 7 is a diagram for explaining a first period, a second period, andswitching timing.

FIG. 8 is a diagram for explaining the relationship between switchingtiming and a first control period and a second control period.

FIG. 9A is a timing chart showing a waveform example in first control,and FIG. 9B is a timing chart showing a waveform example in secondcontrol.

FIG. 10A is a timing chart showing another waveform example in the firstcontrol, and FIG. 10B is a timing chart showing another waveform examplein the second control.

FIG. 11A is a timing chart showing still another waveform example in thefirst control, and FIG. 11B is a timing chart showing still anotherwaveform example in the second control.

FIG. 12 is a diagram for explaining the relationship between switchingtiming and a first control period, a second control period, and a thirdcontrol period.

FIG. 13 is a timing chart showing a waveform example in third control.

FIG. 14 is a flowchart showing a control example of a projector of athird embodiment.

FIG. 15 is a diagram showing an example of the correspondence betweendrive conditions.

FIG. 16 is a diagram showing an example of the correspondence betweendrive conditions.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, a preferred embodiment of the invention will be describedin detail by using the drawings. It should be understood that theembodiment described below is not meant to limit unduly the scope of theinvention claimed in the appended claims in any way, and all theconfigurations described below are not always necessary requirements ofthe invention.

1. Projector According to First Embodiment 1-1. Optical System of theProjector

FIG. 1 is an explanatory diagram showing an optical system of aprojector 500 according to a first embodiment. The projector 500 has alight source device 200, a parallelizing lens 305, an illuminationsystem 310, a color separation system 320, three liquid crystal lightvalves 330R, 330G, and 330B, across dichroic prism 340, and a projectionsystem 350.

The light source device 200 has a light source unit 210 and a dischargelamp lighting device 10. The light source unit 210 has a main reflectionmirror 112, a sub-reflection mirror 50 (which will be described later),and a discharge lamp 90. The discharge lamp lighting device 10 suppliespower to the discharge lamp 90 and turns on the discharge lamp 90. Themain reflection mirror 112 reflects the light emitted from the dischargelamp 90 in a direction of radiation D. The direction of radiation D isparallel to an optical axis AX. The light from the light source unit 210passes through the parallelizing lens 305 and enters the illuminationsystem 310. The parallelizing lens 305 parallelizes the light from thelight source unit 210.

The illumination system 310 makes the illuminance of the light from thelight source device 200 uniform in the liquid crystal light valves 330R,330G, and 330B. Moreover, the illumination system 310 makes the lightfrom the light source device 200 have one polarization direction to makeeffective use of the light from the light source device 200 in theliquid crystal light valves 330R, 330G, and 330B. The light whoseilluminance distribution and polarization direction have been adjustedenters the color separation system 320. The color separation system 320separates the incident light into three colored lights: a red (R) light,a green (G) light, and a blue (B) light. The three colored lights aremodulated by the liquid crystal light valves 330R, 330G, and 330B, eachbeing related to a corresponding one of the three colors. The liquidcrystal light valves 330R, 330G, and 330B include liquid crystal panels560R, 560G, and 560E (which will be described later) and polarizers (notshown) which are disposed on light incident-sides and light-exitingsides of the liquid crystal panels 560R, 560G, and 560B. The threemodulated colored lights are combined by the cross dichroic prism 340.The combined light enters the projection system 350. The projectionsystem 350 projects the incident light onto an unillustrated screen. Asa result, an image is displayed on the screen.

Incidentally, as the configurations of the parallelizing lens 305, theillumination system 310, the color separation system 320, the crossdichroic prism 340, and the projection system 350, various well-knownconfigurations can be adopted.

FIG. 2 is an explanatory diagram showing the configuration of the lightsource device 200. The light source device 200 has the light source unit210 and the discharge lamp lighting device 10. In the drawing, asectional view of the light source unit 210 is shown. The light sourceunit 210 has the main reflection mirror 112, the discharge lamp 90, andthe sub-reflection mirror 50.

The discharge lamp 90 has a rod-like shape extending from a first end 90e 1 to a second end 90 e 2 in the direction of radiation D. The materialof the discharge lamp 90 is, for example, a light-transmissive materialsuch as silica glass. The discharge lamp 90 has a spherical bulge in thecenter thereof. Inside the spherical bulge, a discharge space 91 isformed. In the discharge space 91, gas which is a discharge mediumcontaining mercury, a rare gas, a metal halide compound, and the like isencapsulated.

The discharge lamp 90 includes a first electrode 92 and a secondelectrode 93. In an example shown in FIG. 2, the first electrode 92 andthe second electrode 93 are provided so as to jut into the dischargespace 91. The first electrode 92 is disposed on the side of thedischarge space 91 which is closer to the first end 90 e 1, and thesecond electrode 93 is disposed on the side of the discharge space 91which is closer to the second end 90 e 2. The first electrode 92 and thesecond electrode 93 have a rod-like shape extending along the opticalaxis AX. In the discharge space 91, the electrode tips (also referred toas the “discharge ends”) of the first electrode and the second electrode93 face each other with a predetermined distance kept between them.Incidentally, the material of the first electrode 92 and the secondelectrode 93 is, for example, metal such as tungsten.

At the first end 90 e 1 of the discharge lamp 90, a first terminal 536is provided. The first terminal 536 and the first electrode 92 areelectrically connected by a conductive member 534 passing through thedischarge lamp 90. Similarly, at the second end 90 e 2 of the dischargelamp 90, a second terminal 546 is provided. The second terminal 546 andthe second electrode 93 are electrically connected by a conductivemember 544 passing through the discharge lamp 90. The material of thefirst terminal 536 and the second terminal 546 is, for example, metalsuch as tungsten. Moreover, as the conductive members 534 and 544,molybdenum foil, for example, is used. The first terminal 536 and thesecond terminal 546 are connected to the discharge lamp lighting device10. The discharge lamp lighting device 10 supplies, to the firstterminal 536 and the second terminal 546, a drive current that drivesthe discharge lamp 90. As a result, arc discharge occurs between thefirst electrode 92 and the second electrode 93. As indicated by dashedarrows, the light (the discharge light) generated by the arc dischargeis emitted in all directions from the discharge position.

To the first end 90 e 1 of the discharge lamp 90, the main reflectionmirror 112 is fixed by a fixing member 114. The shape of a reflectingsurface (a surface on the side facing the discharge lamp 90) of the mainreflection mirror 112 is spheroidal. The main reflection mirror 112reflects the discharge light in the direction of radiation D.Incidentally, the shape of the reflecting surface of the main reflectionmirror 112 is not limited to a spheroidal shape, and various shapes bywhich the discharge light is reflected in the direction of radiation Dcan be adopted. For example, a rotated parabola-like shape may beadopted. In this case, the main reflection mirror 112 can convert thedischarge light into a light which is nearly parallel to the opticalaxis AX. Therefore, it is possible to omit the parallelizing lens 305.On the side of the discharge lamp 90 which is closer to the second end90 e 2, the sub-reflection mirror 50 is fixed by a fixing member 522. Areflecting surface (a surface on the side facing the discharge lamp 90)of the sub-reflection mirror 50 has a spherical shape surrounding theside of the discharge space 91 which is closer to the second end 90 e 2.The sub-reflection mirror 50 reflects the discharge light toward themain reflection mirror 112. This makes it possible to increase the usageefficiency of the light emitted from the discharge space 91.

Incidentally, as the material of the fixing members 114 and 522, anyheat-resistant material (for example, an inorganic adhesive) that isresistant to heat generated by the discharge lamp 90 can be adopted.Moreover, the method for fixing the placement of the main reflectionmirror 112, the sub-reflection mirror 50, and the discharge lamp 90 isnot limited to the method by which the main reflection mirror 112 andthe sub-reflection mirror 50 are fixed to the discharge lamp 90, and anymethod can be adopted. For example, the discharge lamp 90 and the mainreflection mirror 112 may be independently fixed to a housing (notshown) of the projector. The same goes for the sub-reflection mirror 50.

1-2. Circuit Configuration of the Projector

FIG. 3 is a diagram showing an example of a circuit configuration of theprojector according to the first embodiment. In addition to the opticalsystems described earlier, the projector 500 may include an image signalconverting section 510, a direct-current power supply device 80, thedischarge lamp lighting device 10, the discharge lamp 90, the liquidcrystal panels 560R, 560G, and 560B, an image processing apparatus 570,and a CPU (central processing unit) 580. Moreover, the projector canalso be configured as a projector system 400 including the projector 500and active shutter glasses 410.

The image signal converting section 510 converts an image signal 502(such as a luminance-color difference signal or an analog RGB signal)input from the outside into a digital RGB signal with a predeterminedword length, generates image signals 512R, 512G, and 512B, and suppliesthe signals to the image processing apparatus 570. Moreover, when apicture signal in which a picture alternates between a first picture anda second picture with given switching timing is input as the imagesignal 502, the image signal converting section 510 supplies asynchronizing signal 514 to the CPU 580 based on the switching timingwith which switching between the first picture and the second picture isperformed.

The image processing apparatus 570 performs image processing on thethree image signals 512R, 512G, and 512B, and supplies, to the liquidcrystal panels 560R, 560G, and 560B, driving signals 572R, 572G, and572B for driving the liquid crystal panels 560R, 560G, and 560B.

The direct-current power supply device 80 converts an alternatingvoltage which is supplied from an external alternating-current powersupply 600 into a constant direct voltage, and supplies the directvoltage to the image signal converting section 510 and the imageprocessing apparatus 570 on the secondary side of a transformer (whichis not shown, but is included in the direct-current power supply device80) and the discharge lamp lighting device 10 on the primary side of thetransformer.

The discharge lamp lighting device 10 forms a discharge path bygenerating a high voltage between the electrodes of the discharge lamp90 at the time of startup and thereby producing a dielectric breakdown,and then supplies a drive current I by which the discharge lamp 90maintains the discharge.

The liquid crystal panels 560R, 560G, and 560B each modulate theintensity of the colored light which enters each liquid crystal panelvia the optical systems described earlier based on the driving signals572R, 572G, and 572B.

The CPU 580 controls the operation of the projector after the projectoris turned on until it is turned off. For example, the CPU 580 mayoutput, to the discharge lamp lighting device 10, an instruction to turnon the discharge lamp or an instruction to turnoff the discharge lampvia a communication signal 582. Moreover, the CPU 580 may receivelighting information of the discharge lamp 90 from the discharge lamplighting device 10 via a communication signal 584. Furthermore, based onthe synchronizing signal 514, the CPU 580 may output, to the activeshutter glasses 410, a control signal 586 for controlling the activeshutter glasses 410 in synchronization with the image signal 502 via awired or wireless communication unit.

The active shutter glasses 410 may include a right shutter 412 and aleft shutter 414. The right shutter 412 and the left shutter 414 arecontrolled so as to be opened and closed based on the control signal586. When the user wears the active shutter glasses 410, the righteye's-side field of view can be blocked as a result of the right shutter412 being closed. Moreover, when the user wears the active shutterglasses 410, the left eye's-side field of view can be blocked as aresult of the left shutter 414 being closed. The right shutter 412 andthe left shutter 414 may be formed as a liquid crystal shutter, forexample.

1-3. Configuration of the Discharge Lamp Lighting Device

FIG. 4 is a diagram showing an example of a circuit configuration of thedischarge lamp lighting device 10.

The discharge lamp lighting device 10 includes a power control circuit20. The power control circuit 20 generates drive power which is suppliedto the discharge lamp 90. In the first embodiment, the power controlcircuit 20 is formed as a step-down chopper circuit that uses adirect-current power supply 80 as an input and outputs a direct currentId by stepping down the input voltage.

The power control circuit 20 can be configured so as to include a switchelement 21, a diode 22, a coil 23, and a capacitor 24. The switchelement 21 can be formed of a transistor, for example. In the firstembodiment, one end of the switch element 21 is connected to a positivevoltage side of the direct-current power supply 80, and the other end isconnected to a cathode terminal of the diode 22 and one end of the coil23. Moreover, to the other end of the coil 23, one end of the capacitor24 is connected, and the other end of the capacitor 24 is connected toan anode terminal of the diode 22 and a negative voltage side of thedirect-current power supply 80. A current control signal is input to acontrol terminal of the switch element 21 from a control section 40(which will be described later), whereby on/off of the switch element 21is controlled. As the current control signal, a PWM (pulse widthmodulation) control signal, for example, may be used.

Here, when the switch element 21 turns on, a current flows through thecoil 23 and energy is accumulated in the coil 23. Then, when the switchelement 21 turns off, the energy accumulated in the coil 23 is releasedin a path passing through the capacitor 24 and the diode 22. As aresult, the direct current Id commensurate with the proportion of theamount of time the switch element 21 is on is generated.

The discharge lamp lighting device 10 includes a polarity reversalcircuit 30. The polarity reversal circuit 30 receives, as an input, thedirect current Id output from the power control circuit 20 and reversesthe polarity with given timing, and thereby generates and outputs thedrive current I which is a direct current that continues only for acontrolled time or an alternating current of any frequency. In the firstembodiment, the polarity reversal circuit 30 is formed as an inverterbridge circuit (a full-bridge circuit).

The polarity reversal circuit 30 includes, for example, a first switchelement 31, a second switch element 32, a third switch element 33, and afourth switch element 34 which are formed of a transistor or the like,and is formed by connecting, in parallel with each other, the firstswitch element 31 and the second switch element 32 which are connectedin series and the third switch element 33 and the fourth switch element34 which are connected in series. To the control terminals of the firstswitch element 31, the second switch element 32, the third switchelement 33, and the fourth switch element 34, a polarity reversalcontrol signal is input from the control section 40, and on/off of thefirst switch element 31, the second switch element 32, the third switchelement 33, and the fourth switch element 34 is controlled based on thepolarity reversal control signal.

The polarity reversal circuit 30 alternately reverses the polarity ofthe direct current Id which is output from the power control circuit 20by alternately turning on/off the first switch element 31 and the fourthswitch element 34 and the second switch element 32 and the third switchelement 33, and generates and outputs the drive current I which is adirect current that continues only for a controlled time or analternating current of a controlled frequency from a common junctionpoint of the first switch element 31 and the second switch element 32and a common junction point of the third switch element 33 and thefourth switch element 34.

That is, control is performed so that, when the first switch element 31and the fourth switch element 34 are on, the second switch element 32and the third switch element 33 are turned off, and, when the firstswitch element 31 and the fourth switch element 34 are off, the secondswitch element 32 and the third switch element 33 are turned on.Therefore, when the first switch element 31 and the fourth switchelement 34 are on, the drive current I flowing from one end of thecapacitor 24 to the fourth switch element 34 via the first switchelement 31 and the discharge lamp 90 in this order is generated.Moreover, when the second switch element 32 and the third switch element33 are on, the drive current I flowing from one end of the capacitor 24to the second switch element 32 via the third switch element 33 and thedischarge lamp 90 in this order is generated.

In the first embodiment, the power control circuit 20 and the polarityreversal circuit 30 collectively correspond to a discharge lamp drivingsection 230. That is, the discharge lamp driving section 230 supplies,to the discharge lamp 90, the drive current I that drives the dischargelamp 90.

The discharge lamp lighting device 10 includes the control section 40.The control section 40 controls the discharge lamp driving section 230.In an example shown in FIG. 4, the control section 40 controls the powercontrol circuit 20 and the polarity reversal circuit 30 and therebycontrols the holding time for which the drive current I with the samepolarity continues and the current value, frequency, etc. of the drivecurrent I. The control section 40 performs polarity polarity reversalcontrol on the polarity reversal circuit 30 so as to control the holdingtime for which the drive current I with the same polarity continues andthe frequency etc. of the drive current I by polarity reversal timing ofthe drive current I. Moreover, the control section 40 performs currentcontrol on the power control circuit 20 so as to control the currentvalue of the direct current Id which is output from the power controlcircuit 20.

The configuration of the control section 40 is not limited to aparticular configuration. In the first embodiment, the control section40 includes a system controller 41, a power control circuit controller42, and a polarity reversal circuit controller 43. Incidentally, part orall of the control section 40 may be formed of a semiconductorintegrated circuit. The system controller 41 controls the power controlcircuit controller 42 and the polarity reversal circuit controller 43and thereby controls the power control circuit 20 and the polarityreversal circuit 30. The system controller 41 may control the powercontrol circuit controller 42 and the polarity reversal circuitcontroller 43 based on a drive voltage Vla which is detected by avoltage detecting section 60, which will be described later, provided inthe discharge lamp lighting device 10 and the drive current I.

In the first embodiment, the system controller 41 includes a storingsection 44. Incidentally, the storing section 44 may be providedindependently of the system controller 41.

The system controller 41 may control the power control circuit 20 andthe polarity reversal circuit 30 based on the information stored in thestoring section 44. In the storing section 44, for example, theinformation on drive parameters such as the holding time for which thedrive current I with the same polarity continues and the current value,frequency, waveform, modulation pattern, etc. of the drive current I maybe stored. The power control circuit controller 42 controls the powercontrol circuit 20 by outputting the current control signal to the powercontrol circuit 20 based on a control signal from the system controller41.

The polarity reversal circuit controller 43 controls the polarityreversal circuit 30 by outputting the polarity reversal control signalto the polarity reversal circuit 30 based on the control signal from thesystem controller 41. Incidentally, the control section 40 can perform,by a dedicated circuit, the above-described control and various kinds ofcontrol of processing which will be described later, but the controlsection 40 can also perform various kinds of control of the processingby functioning as a computer as a result of a CPU (central processingunit), for example, executing a control program product stored in thestoring section 44 or the like. FIG. 5 is a diagram for explaininganother configuration example of the control section 40. As shown inFIG. 5, the control section 40 may be configured so as to function, bythe control program product, as a current control unit 40-1 thatcontrols the power control circuit 20 and a polarity reversal controlunit 40-2 that controls the polarity reversal circuit 30.

Moreover, in the example shown in FIG. 4, the control section 40 isconfigured as part of the discharge lamp lighting device 10; however,the control section 40 may also be configured so that the CPU 580shoulders part of the function of the control section 40.

The discharge lamp lighting device 10 may include an operation detectingsection. The operation detecting section may include, for example, thevoltage detecting section 60 that detects the drive voltage Vla of thedischarge lamp 90 and outputs drive voltage information or a currentdetecting section that detects the drive current I and outputs drivecurrent information. In this embodiment, the voltage detecting section60 includes first and second resistances 61 and 62.

The voltage detecting section 60 corresponds to a state detectingsection in the invention. That is, the state detecting section (thevoltage detecting section 60) detects the drive voltage Vla as a valueindicating the degree of deterioration of the electrode.

In the first embodiment, the voltage detecting section 60 detects thedrive voltage Vla based on a voltage obtained by voltage dividingperformed by the first resistance 61 and the second resistance 62 whichare connected in series and are connected in parallel with the dischargelamp 90. Moreover, in the first embodiment, the current detectingsection detects the drive current I based on a voltage which isgenerated in a third resistance 63 connected in series with thedischarge lamp 90.

The discharge lamp lighting device 10 may include an ignitor circuit 70.The ignitor circuit 70 operates only when the discharge lamp 90 isturned on and supplies, between the electrodes of the discharge lamp 90(between the first electrode 92 and the second electrode 93), a highvoltage (a voltage which is higher than the voltage observed when thedischarge lamp 90 is in a normal on state) necessary for forming adischarge path by producing a dielectric breakdown between theelectrodes of the discharge lamp 90 (between the first electrode 92 andthe second electrode 93) when the discharge lamp 90 is turned on. In thefirst embodiment, the ignitor circuit 70 is connected in parallel withthe discharge lamp 90.

1-4. Relationship Between the Polarity of the Drive Current and theTemperature of the Electrode

FIGS. 6A to 6D are explanatory diagrams showing the relationship betweenthe polarity of the drive current I which is supplied to the dischargelamp 90 and the temperature of the electrode. FIGS. 6A and 6B show theoperation states of the first electrode 92 and the second electrode 93.In the drawings, the tip portions of the first electrode 92 and thesecond electrode 93 are shown. At the tips of the first electrode 92 andthe second electrode 93, projections 552 p and 562 p are provided. Thedischarge which occurs between the first electrode 92 and the secondelectrode 93 mainly occurs between the projection 552 p and theprojection 562 p. In this embodiment, it is possible to prevent themovement of the discharge positions (the arc positions) in the firstelectrode 92 and the second electrode 93 as compared to when noprojection is provided. However, such projections may be omitted.

FIG. 6A shows a first polarity state P1 in which the first electrode 92operates as a positive electrode and the second electrode 93 operates asa negative electrode. In the first polarity state P1, electrons movefrom the second electrode (the negative electrode) to the firstelectrode 92 (the positive electrode) by discharge. The electrons arereleased from the negative electrode (the second electrode 93). Theelectrons released from the negative electrode (the second electrode 93)collide with the tip of the positive electrode (the first electrode 92).Heat is generated by this collision, and the temperature of the tip (theprojection 552 p) of the positive electrode (the first electrode 92)rises.

FIG. 6B shows a second polarity state P2 in which the first electrode 92operates as a negative electrode and the second electrode 93 operates asa positive electrode. In the second polarity state P2, unlike the firstpolarity state P1, the electrons move from the first electrode 92 to thesecond electrode 93. As a result, the temperature of the tip (theprojection 562 p) of the second electrode 93 rises.

As described above, the temperature of the positive electrode is morelikely to increase than the negative electrode. Here, if a state inwhich the temperature of one electrode is higher than the temperature ofthe other electrode continues, various malfunctions can occur. Forexample, when the tip of the high-temperature electrode is excessivelymelted, an unintended electrode deformation can appear. As a result, thearc length may deviate from an appropriate value. Moreover, when the tipof the low-temperature electrode is melted inadequately, minutesprojections and depressions which have appeared in the tip can remainwithout being melted. As a result, so-called arc jump (a phenomenon inwhich the arc position becomes unstable and moves) may occur.

As a technique to prevent such malfunctions, AC drive by which thepolarity of each electrode is repeatedly changed can be used. FIG. 6C isa timing chart showing an example of the drive current I which issupplied to the discharge lamp 90 (FIG. 2). The horizontal axisrepresents time T and the vertical axis represents the current value ofthe drive current I. The drive current I represents a current flowingthrough the discharge lamp 90. The positive value represents the firstpolarity state P1 and the negative value represents the second polaritystate P2. In an example shown in FIG. 6C, a rectangular wave alternatingcurrent is used as the drive current I. In addition, in the exampleshown in FIG. 6C, the first polarity state P1 and the second polaritystate P2 are repeated alternately. Here, a first polarity interval Tprepresents the time for which the first polarity state P1 continues, anda second polarity interval Tn represents the time for which the secondpolarity state P2 continues. Moreover, in the example shown in FIG. 6C,the average current value of the first polarity interval Tp is Im1, andthe average current value of the second polarity interval Tn is −Im2.Incidentally, the frequency of the drive current I appropriate for thedriving of the discharge lamp 90 can be experimentally determined inaccordance with the characteristics of the discharge lamp 90 (forexample, a value in the 30 Hz-to-1 kHz range is adopted). The othervalues Im1, −Im2, Tp, and Tn can also be experimentally determined.

FIG. 6D is a timing chart showing a change in the temperature of thefirst electrode 92. The horizontal axis represents time T and thevertical axis represents the temperature H. In the first polarity stateP1, the temperature H of the first electrode 92 rises; in the secondpolarity state P2, the temperature H of the first electrode 92 falls.Moreover, since the first polarity state P1 and the second polaritystate P2 are repeated, the temperature H varies periodically between theminimum value Hmin and the maximum value Hmax. Though not shown in thedrawing, the temperature of the second electrode 93 varies in a phaseopposite to that of the temperature H of the first electrode 92. Thatis, in the first polarity state P1, the temperature of the secondelectrode 93 falls; in the second polarity state P2, the temperature ofthe second electrode 93 rises.

In the first polarity state P1, the tip of the first electrode 92 (theprojection 552 p) is melted, whereby the tip of the first electrode 92(the projection 552 p) becomes smooth. This makes it possible to preventthe movement of the discharge position in the first electrode 92.Moreover, since the temperature of the tip of the second electrode 93(the projection 562 p) falls, the second electrode 93 (the projection562 p) is prevented from being excessively melted. This makes itpossible to prevent unintended electrode deformation. In the secondpolarity state P2, the situations of the first electrode 92 and thesecond electrode 93 are opposite to those described above. Therefore, byrepeating the two states P1 and P2, it is possible to prevent themalfunctions in the first electrode 92 and the second electrode 93.

Here, when the waveform of the drive current I is symmetrical, that is,when the waveform of the drive current I meets the conditions that“|Im1=|=|−Im2| and Tp=Tn”, the first electrode 92 and the secondelectrode 93 are the same in condition of the supplied power. Therefore,when the first electrode 92 and the second electrode 93 are the same inthermal condition (the temperature's readiness to rise or fall), it isestimated that the temperature difference between the first electrode 92and the second electrode 93 becomes smaller.

Moreover, when a wide range of the electrode is excessively heated (whenan arc spot (a hot spot on the surface of the electrode associated witharc discharge) becomes larger), the electrode loses its shape due toexcessive melting. On the other hand, when the electrode is excessivelycooled (when the arc spot becomes smaller), it becomes impossible tomelt the tip of the electrode adequately, whereby the tip cannot berestored to a smooth state, that is, the tip of the electrode tends tobe deformed. Therefore, when a state in which energy is uniformlysupplied to the electrodes continues, the tips (the projection 552 p andthe projection 562 p) of the electrodes tend to be deformed intounintended shapes.

1-5. Example of Control of the Drive Current

Next, a specific example of control of the drive current I in theprojector 500 according to the first embodiment will be described.

FIG. 7 is a diagram for explaining a first period, a second period, andswitching timing. In FIG. 7, from above, the contents of the drivingsignals 572R, 572G, and 572B, the open and closed state of the rightshutter 412, the open and closed state of the left shutter 414, and thetemporal relationship between the first period and the second period andswitching timing are shown. The horizontal axis of FIG. 7 representstime. Hereinafter, an example in which the observer is made to view adisplay picture stereoscopically by using the first picture and thesecond picture as a picture for the right eye and a picture for the lefteye, respectively, will be described. In an example shown in FIG. 7, thedriving signals 572R, 572G, and 572B are driving signals correspondingto the picture for the right eye as the first picture from time t1 totime t3, the picture for the left eye as the second picture from time t3to time t5, the picture for the right eye as the first picture from timet5 to time t7, and the picture for the left eye as the second picturefrom time t7 to time t9. Therefore, in the example shown in FIG. 7, theprojector 500 outputs the picture for the right eye as the first pictureand the picture for the left eye as the second picture alternately whileperforming switching between them by using time t1, time t3, time t5,time t7, and time t9 as time at which switching is performed.

A period sandwiched between a time at which switching is performed andthe next time at which switching is performed starts with the firstperiod and ends with the second period. In the example shown in FIG. 7,for example, a period sandwiched between time t1 and time t3, at whichswitching is performed, starts with the first period from time t1 totime t2 and ends with the second period from time t2 to time t3. Thesame goes for a period sandwiched between time t3 and time t5, at whichswitching is performed, a period sandwiched between time t5 and time t7,at which switching is performed, and a period sandwiched between time t7and time t9, at which switching is performed. Incidentally, in theexample shown in FIG. 7, the first period and the second period have thesame length; however, the length of the first period and the length ofthe second period can be appropriately set as needed. Moreover, a thirdperiod may exist between the first period and the second period. In thethird period, control which is different from the control of the drivecurrent I in the first period and the second period, which will bedescribed later, may be performed.

The right shutter 412 is in an open state in a period which is at leastpart of the period in which the driving signals 572R, 572G, and 572Bcorresponding to the picture for the right eye as the first picture areinput to the liquid crystal panels 560R, 560G, and 560B. In the exampleshown in FIG. 7, the right shutter 412 is in a closed state from time t1to time t2 and is in an open state from time t2 to time t3. Moreover, inthe example shown in FIG. 7, in the period in which the driving signals572R, 572G, and 572B corresponding to the picture for the left eye asthe second picture are input to the liquid crystal panels 560R, 560G,and 560B, the right shutter 412 starts to close from time t3, iscompletely closed between time t3 and time t4, and is in a closed statefrom time t4 to time t5. A change in the open and closed state of theright shutter 412 from time t5 to time t9 is the same as a change in theopen and closed state from time t1 to time t5.

The left shutter 414 is in an open state in a period which is at leastpart of the period in which the driving signals 572R, 572G, and 572Bcorresponding to the picture for the left eye as the second picture areinput to the liquid crystal panels 560R, 560G, and 560B. In the exampleshown in FIG. 7, the left shutter 414 is in a closed state from time t3to time t4 and is in an open state from time t4 to time t5. Moreover, inthe example shown in FIG. 7, in the period in which the driving signals572R, 572G, and 572B corresponding to the picture for the right eye asthe first picture are input to the liquid crystal panels 560R, 560G, and560B, the left shutter 414 starts to close from time t1, is completelyclosed between time t1 and time t2, and is in a closed state from timet2 to time t3. A change in the open and closed state of the left shutter414 from time t5 to time t9 is the same as a change in the open andclosed state from time t1 to time t5.

In the example shown in FIG. 7, in the period in which the drivingsignals 572R, 572G, and 572B corresponding to the picture for the righteye as the first picture are input to the liquid crystal panels 560R,560G, and 560B, a period in which the right shutter 412 is closedcorresponds to the first period and a period in which the right shutter412 is open corresponds to the second period. Moreover, in the exampleshown in FIG. 7, in the period in which the driving signals 572R, 572G,and 5723 corresponding to the picture for the left eye as the secondpicture are input to the liquid crystal panels 560R, 560G, and 560B, aperiod in which the left shutter 414 is closed corresponds to the firstperiod and a period in which the left shutter 414 is open corresponds tothe second period. Furthermore, in the example shown in FIG. 7, in thefirst period, a period in which both the right shutter 412 and the leftshutter 414 are closed exists.

FIG. 8 is a diagram for explaining the relationship between switchingtiming and a first control period and a second control period. Thehorizontal axis of FIG. 8 represents time. Moreover, times t11 to t27are times at which switching is performed. The first control period is aperiod in which the control section 40 performs first control, and thesecond control period is a period in which the control section 40performs second control.

In the projector 500 according to the first embodiment, the controlsection 40 performs the first control in the first control period whichcontinues at least for a period sandwiched between a time at whichswitching is performed and the next time at which switching isperformed, and performs the second control in the second control periodwhich continues at least for a period sandwiched between a time at whichswitching is performed and the next time at which switching isperformed, the second control period different from the first controlperiod. In an example shown in FIG. 8, the first control and the secondcontrol continue for a period which is four times longer than the periodsandwiched between a time at which switching is performed and the nexttime at which switching is performed. For example, in FIG. 8, an initialfirst control period continues for a period from time t11 which is atime at which switching is performed to time t15 which is a time atwhich switching is performed. Moreover, in FIG. 8, an initial secondcontrol period continues for a period from time t15 which is a time atwhich switching is performed to time t19 which is a time at whichswitching is performed. Incidentally, the length of time for which thefirst control continues and the length of time for which the secondcontrol continues can be appropriately set in accordance with thespecifications of the discharge lamp 90.

FIG. 9A is a timing chart showing a waveform example in the firstcontrol, and FIG. 9B is a timing chart showing a waveform example in thesecond control. The horizontal axes of FIGS. 9A and 9B represent timeand the vertical axes represent the current value of the drive currentI. Moreover, in FIGS. 9A and 9B, the drive current I when the firstelectrode 92 is a positive electrode is shown as a positive value, andthe drive current I when the second electrode 93 is a positive electrodeis shown as a negative value. Furthermore, in the following description,the polarity of the drive current I when the first electrode 92 is apositive electrode is expressed as a first polarity, and the polarity ofthe drive current I when the second electrode 93 is a positive electrodeis expressed as a second polarity.

In the projector 500 according to the first embodiment, in the firstcontrol and the second control, the control section 40 controls thedischarge lamp driving section 230 so that the absolute value of thedrive current I in the first period becomes relatively small as comparedto that in the second period and the absolute value of the drive currentI in the second period becomes relatively large as compared to that inthe first period.

In an example shown in FIG. 9A, the absolute value of the current valueof the drive current I is I1 in the first period and I2 in the secondperiod. Moreover, in the example shown in FIG. 9A, I1<I2. Therefore, inthe first control, the absolute value of the drive current I isrelatively small in the first period and relatively large in the secondperiod.

Similarly, in an example shown in FIG. 9B, the absolute value of thecurrent value of the drive current I is I1 in the first period and I2 inthe second period. Moreover, in the example shown in FIG. 9B, I1<I2.Therefore, in the second control, the absolute value of the drivecurrent I is relatively small in the first period and relatively largein the second period. In the examples shown in FIGS. 9A and 9B, theabsolute value of the drive current I in the first period and theabsolute value of the drive current I in the second period are constantin each period; however, the invention is not limited thereto. Forexample, when the absolute value of the drive current I in the firstperiod and the absolute value of the drive current I in the secondperiod vary in each period, the control section 40 may control thedischarge lamp driving section 230 so that the average value of theabsolute values of the drive current I in each period becomes relativelysmall in the first period and relatively large in the second period.Moreover, for example, when the absolute value of the drive current I inthe first period and the absolute value of the drive current I in thesecond period vary in each period, the control section 40 may controlthe discharge lamp driving section 230 so as to take the minimum valueof the absolute value of the drive current I, in the first period andtake the maximum value of the absolute value of the drive current I inthe second period. In the projector 500 according to the firstembodiment, in the first control, in the first period, the controlsection 40 controls the discharge lamp driving section 230 so that thedischarge lamp driving section 230 supplies an alternating current tothe discharge lamp 90 as the drive current I. The alternating current isa current with alternating first polarity and second polarity. In theexample shown in FIG. 9A, the control section 40 controls the dischargelamp driving section 230 so that the discharge lamp driving section 230generates an alternating current corresponding to one period byreversing the polarity with the absolute value of the current value ofthe drive current I kept constant in the first period and supplies thealternating current to the discharge lamp 90 as the drive current I.Moreover, in the example shown in FIG. 9A, an alternating current offour periods is supplied to the discharge lamp 90 as the drive current Iin one first period. The frequency of the alternating current can beexperimentally determined in accordance with the characteristics of thedischarge lamp 90. For example, the frequency of the alternating currentmay be selected in the 30 Hz-to-1 kHz range. In the projector 500according to the first embodiment, in the first control, in the secondperiod, the control section 40 performs first control processing bywhich the control section 40 controls the discharge lamp driving section230 so that the discharge lamp driving section 230 supplies, to thedischarge lamp 90, the drive current I by which the energy provided tothe first electrode 92 in the second period becomes greater than theenergy provided to the second electrode 93 in the second period.

In the example shown in FIG. 9A, in the first control processing, thecontrol section 40 controls the discharge lamp driving section 230 sothat the discharge lamp driving section 230 supplies, to the dischargelamp 90, a direct current by which the first electrode becomes apositive electrode as the drive current I. The direct current by whichthe first electrode becomes a positive electrode is a current thatstarts with the first polarity and is formed of a current with the firstpolarity. In the example shown in FIG. 9A, the control section 40controls the discharge lamp driving section 230 so that the dischargelamp driving section 230 supplies, to the discharge lamp 90, a directcurrent which is a current obtained by making the absolute value of thecurrent value of the drive current I constant in the second period asthe drive current I. This makes it possible to realize the first controlprocessing with simple control.

In the projector 500 according to the first embodiment, in the secondcontrol, in the first period, the control section 40 controls thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, an alternating currentas the drive current I. In the example shown in FIG. 9B, the controlsection 40 controls the discharge lamp driving section 230 so that thedischarge lamp driving section 230 generates an alternating currentcorresponding to one period by reversing the polarity with the absolutevalue of the current value of the drive current I kept constant in thefirst period and supplies the alternating current to the discharge lamp90 as the drive current I. Moreover, in the example shown in FIG. 9B, analternating current of four periods is supplied to the discharge lamp 90as the drive current I in one first period. The frequency of thealternating current can be experimentally determined in accordance withthe characteristics of the discharge lamp 90. For example, the frequencyof the alternating current may be selected in the 30 Hz-to-1 kHz range.

In the projector 500 according to the first embodiment, in the secondperiod, the control section 40 performs second control processing bywhich the control section 40 controls the discharge lamp driving section230 so that the discharge lamp driving section 230 supplies, to thedischarge lamp 90, the drive current I by which the energy provided tothe second electrode 93 in the second period becomes greater than theenergy provided to the first electrode 92 in the second period. In theexample, shown in FIG. 93, in the second control processing, the controlsection 40 controls the discharge lamp driving section 230 so that thedischarge lamp driving section 230 supplies, to the discharge lamp 90, adirect current by which the second electrode becomes a positiveelectrode as the drive current I. The direct current by which the secondelectrode becomes a positive electrode is a current that starts with thesecond polarity and is formed of a current with the second polarity. Inthe example shown in FIG. 9B, the control section 40 controls thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, a direct current whichis a current obtained by making the absolute value of the current valueof the drive current I constant in the second period as the drivecurrent I. This makes it possible to realize the second controlprocessing with simple control.

With the projector 500 according to the first embodiment, since theenergy provided to the first electrode 92 becomes greater in the firstcontrol processing, the fusibility of the first electrode 92 isincreased. Therefore, it is possible to prevent deformation of the firstelectrode 92. Moreover, with the projector 500 according to the firstembodiment, since the energy provided to the second electrode 93 becomesgreater in the second control processing, the fusibility of the secondelectrode 93 is increased. Therefore, it is possible to preventdeformation of the second electrode 93. As a result, by performing thefirst control processing and the second control processing, it ispossible to prevent deformation of the first electrode 92 and the secondelectrode 93.

Moreover, with the projector 500 according to the first embodiment, thecontrol section 40 controls the discharge lamp driving section 230 sothat the absolute value of the drive current I becomes minimum in thefirst period and becomes maximum in the second period. As a result, whenthe projector 500 is driven with the average drive power throughout thefirst period and the second period kept constant, the projector 500 canproject a darker picture than that projected when the projector 500 isdriven by the average drive power in the first period and can project abrighter picture than that projected when the projector 500 is driven bythe average drive power in the second period. In the first period, sincethere is a period in which both the right shutter 412 and the leftshutter 414 are closed, even when the projected picture is dark, thepicture quality is less likely to be affected. On the other hand, in thesecond period, any one of the right shutter 412 and the left shutter 414is in an open state, which makes it possible to make the pictureprojected so that it is viewed by the user appear brighter than when theprojector 500 is driven by the average drive power. In this way, it ispossible to realize a projector that can project a picture in such a waythat the picture appears bright. Moreover, by projecting a picture insuch a way that the picture appears dark in the first period, it ispossible to prevent the occurrence of crosstalk. Furthermore, since theneed for increasing the average drive power to make the picture appearbright is lessened, it is possible to reduce the power consumption ofthe projector. This makes it possible to reduce deterioration ofperipheral parts associated with the increase in average drive power.

In the projector 500 according to the first embodiment, the controlsection 40 may perform second control in a period which is at least partof the period sandwiched between the first control periods which arenext to each other in terms of time. In the example shown in FIG. 8, thefirst control period from time t11 to time t15 and the first controlperiod from time t19 to time t23 are next to each other in terms oftime. A period from time t15 to time t19, the period sandwiched betweenthe two first control periods, is the second control period. That is, inthe example shown in FIG. 8, the entire period sandwiched between thefirst control periods which are next to each other in terms of time isthe second control period. Therefore, in the example shown in FIG. 8,the first control period and the second control period are repeatedalternately. By performing the second control in a period which is atleast part of a period sandwiched between the first control periodswhich are next to each other in terms of time, it is possible to keep aheat load balance between the first electrode 92 and the secondelectrode 93 of the discharge lamp 90. This makes it possible to preventonly one of the electrodes of the discharge lamp from wearing out.

1-6. Modified Example 1

FIG. 10A is a timing chart showing another waveform example in the firstcontrol, and FIG. 10B is a timing chart showing another waveform examplein the second control. The horizontal axes of FIGS. 10A and 10Brepresent time and the vertical axes represent the current value of thedrive current I. Moreover, in FIGS. 10A and 10B, the drive current Iwhen the first electrode 92 is a positive electrode is shown as apositive value, and the drive current I when the second electrode 93 isa positive electrode is shown as a negative value.

The waveform examples shown in FIGS. 9A and 9B differ from the waveformexamples shown in FIGS. 10A and 10B in the waveform in the secondperiod. That is, the first embodiment differs from Modified Example 1 inthe contents of the first control processing and the second controlprocessing, and the first embodiment and Modified Example 1 are the samein other configurations. Therefore, in the following description, onlythe contents of the first control processing and the second controlprocessing will be described.

In an example shown in FIG. 10A, in the first control processing (thefirst control in the second period), the control section 40 controls thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, an alternating currentby which the time in which the first electrode 92 is a positiveelectrode, the time in one period, is longer than the time in which thesecond electrode 93 is a positive electrode as the drive current I. Inthe example shown in FIG. 10A, the control section 40 controls thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 generates an alternating current corresponding to one periodby reversing the polarity with the absolute value of the current valueof the drive current I kept constant in the second period and suppliesthe alternating current to the discharge lamp 90 as the drive current I.Moreover, the control section 40 controls the discharge lamp drivingsection 230 so that the discharge lamp driving section 230 reverses thepolarity of the drive current I with such timing that the time for whichthe first polarity continues is longer than the time for which thesecond polarity continues. This makes it possible to realize the firstcontrol processing with simple control.

Moreover, in an example shown in FIG. 10B, in the second controlprocessing (the second control in the second period), the controlsection 40 controls the discharge lamp driving section 230 so that thedischarge lamp driving section 230 supplies, to the discharge lamp 90,an alternating current by which the time in which the second electrode93 is a positive electrode, the time in one period, is longer than thetime in which the first electrode 92 is a positive electrode as thedrive current I. In the example shown in FIG. 10B, the control section40 controls the discharge lamp driving section 230 so that the dischargelamp driving section 230 generates an alternating current correspondingto one period by reversing the polarity with the absolute value of thecurrent value of the drive current I kept constant in the second periodand supplies the alternating current to the discharge lamp 90 as thedrive current I. Moreover, the control section 40 controls the dischargelamp driving section 230 so that the discharge lamp driving section 230reverses the polarity of the drive current I with such timing that thetime for which the second polarity continues is longer than the time forwhich the first polarity continues. This makes it possible to realizethe second control processing with simple control.

According to Modified Example 1, since the energy provided to the firstelectrode 92 becomes greater in the first control processing, thefusibility of the first electrode 92 is increased. Therefore, it ispossible to prevent deformation of the first electrode 92. Moreover,according to Modified Example 1, since the energy provided to the secondelectrode becomes greater in the second control processing, thefusibility of the second electrode 93 is increased. Therefore, it ispossible to prevent deformation of the second electrode 93. As a result,by performing the first control processing and the second controlprocessing, it is possible to prevent deformation of the first electrode92 and the second electrode 93.

1-7. Modified Example 2

FIG. 1A is a timing chart showing still another waveform example in thefirst control, and FIG. 11B is a timing chart showing still anotherwaveform example in the second control. The horizontal axes of FIGS. 11Aand 11B represent time and the vertical axes represent the current valueof the drive current I. Moreover, in FIGS. 11A and 11B, the drivecurrent I when the first electrode 92 is a positive electrode is shownas a positive value, and the drive current I when the second electrode93 is a positive electrode is shown as a negative value.

The waveform examples shown in FIGS. 9A and 9B differ from the waveformexamples shown in FIGS. 11A and 11B in the waveform in the secondperiod. That is, the first embodiment differs from Modified Example 2 inthe contents of the first control processing and the second controlprocessing, and the first embodiment and Modified Example 2 are the samein other configurations. Therefore, in the following description, onlythe contents of the first control processing and the second controlprocessing will be described.

In an example shown in FIG. 11A, in the first control processing (thefirst control in the second period), the control section 40 controls thedischarge lamp driving section 230 so as to include a period in whichthe discharge lamp driving section 230 supplies an alternating currentas the drive current I and a period in which the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, a direct current bywhich the first electrode 92 becomes a positive electrode as the drivecurrent I. In the example shown in FIG. 11A, in the period in which thedischarge lamp driving section 230 supplies an alternating current, thecontrol section 40 controls the discharge lamp driving section 230 sothat the discharge lamp driving section 230 generates an alternatingcurrent corresponding to one period by reversing the polarity with theabsolute value of the current value of the drive current I kept constantin the second period and supplies the alternating current to thedischarge lamp 90 as the drive current I. Moreover, in the example shownin FIG. 11A, in the period in which the discharge lamp driving section230 supplies a direct current, the control section 40 controls thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, a direct current whichis a current obtained by making the absolute value of the current valueof the drive current I constant in the second period as the drivecurrent I. This makes it possible to realize the first controlprocessing with simple control.

In an example shown in FIG. 11B, in the second control processing (thefirst control in the second period), the control section 40 controls thedischarge lamp driving section 230 so as to include a period in whichthe discharge lamp driving section 230 supplies an alternating currentas the drive current I and a period in which the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, a direct current bywhich the second electrode 93 becomes a positive electrode as the drivecurrent I. In the example shown in FIG. 11B, in the period in which thedischarge lamp driving section 230 supplies an alternating current, thecontrol section 40 controls the discharge lamp driving section 230 sothat the discharge lamp driving section 230 generates an alternatingcurrent corresponding to one period by reversing the polarity with theabsolute value of the current value of the drive current I kept constantin the second period and supplies the alternating current to thedischarge lamp 90 as the drive current I. Moreover, in the example shownin FIG. 11B, in the period in which the discharge lamp driving section230 supplies a direct current, the control section 40 controls thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 supplies, to the discharge lamp 90, a direct current whichis a current obtained by making the absolute value of the current valueof the drive current I constant in the second period as the drivecurrent I. This makes it possible to realize the second controlprocessing with simple control. Incidentally, in the examples shown inFIGS. 11A and 11B, the control by which an alternating current issupplied at the start of the second period and a direct current issupplied at the end of the second period is performed; however, analternating current and a direct current may be supplied in any order.According to Modified Example 2, since the energy provided to the firstelectrode 92 becomes greater in the first control processing, thefusibility of the first electrode 92 increased. Therefore, it ispossible to prevent deformation of the first electrode 92. Moreover,according to Modified Example 2, since the energy provided to the secondelectrode becomes greater in the second control processing, thefusibility of the second electrode 93 is increased. Therefore, it ispossible to prevent deformation of the second electrode 93. As a result,by performing the first control processing and the second controlprocessing, it is possible to prevent deformation of the first electrode92 and the second electrode 93.

2. Projector According to Second Embodiment

Next, a projector 500 according to a second embodiment will bedescribed. The configurations of the optical systems and the circuits ofthe projector 500 according to the second embodiment are the same asthose of the projector 500 according to the first embodiment. Therefore,in the following description, a specific example of control of the drivecurrent I in the projector 500 according to the second embodiment willbe described. Incidentally, the contents of the driving signals 572R,572G, and 572B, the open and closed state of the right shutter 412, theopen and closed state of the left shutter 414, and the temporalrelationship between the first period and the second period andswitching timing have already been described by using FIG. 7.

FIG. 12 is a diagram for explaining the relationship between switchingtiming and a first control period, a second control period, and a thirdcontrol period. The horizontal axis of FIG. 12 represents time.Moreover, times t11 to t27 are times at which switching is performed.The first control period is a period in which the control section 40performs first control, the second control period is a period in whichthe control section 40 performs second control, and the third controlperiod is a period in which the control section 40 performs thirdcontrol. Incidentally, the contents of the first control and the secondcontrol are the same as those of the first embodiment, and therefore adetailed description thereof is omitted.

In the projector 500 according to the second embodiment, the controlsection 40 performs the third control in a third control period whichcontinues at least for a period sandwiched between a time at whichswitching is performed and the next time at which switching isperformed, the third control period different from the first controlperiod and the second control period. In an example shown in FIG. 12,the first control, the second control, and the third control continuefor a period which is twice as long as the period sandwiched between atime at which switching is performed and the next time at whichswitching is performed. For example, in FIG. 12, an initial firstcontrol period continues for a period from time t13 which is a time atwhich switching is performed to time t15 which is a time at whichswitching is performed. Moreover, in FIG. 12, an initial second controlperiod continues for a period from time t17 which is a time at whichswitching is performed to time t19 which is a time at which switching isperformed. Furthermore, in FIG. 12, an initial third control periodcontinues for a period from time t11 which is a time at which switchingis performed to time t13 which is a time at which switching isperformed. Incidentally, the length of time for which the first controlcontinues, the length of time for which the second control continues,and the length of time for which the third control continues can beappropriately set in accordance with the specifications of the dischargelamp 90. FIG. 13 is a timing chart showing a waveform example in thethird control. The horizontal axis of FIG. 13 represents time and thevertical axis represents the current value of the drive current I.Moreover, in FIG. 13, the drive current I when the first electrode 92 isa positive electrode is shown as a positive value, and the drive currentI when the second electrode 93 is a positive electrode is shown as anegative value.

In the projector 500 according to the second embodiment, in the thirdcontrol, the control section 40 controls the discharge lamp drivingsection 230 so that the absolute value of the drive current I in thefirst period becomes relatively small as compared to that in the secondperiod and the absolute value of the drive current I in the secondperiod becomes relatively large as compared to that in the first period.

In an example shown in FIG. 13, the absolute value of the current valueof the drive current I is I1 in the first period and I2 in the secondperiod. Moreover, in the example shown in FIG. 13, I1<I2. Therefore, inthe third control, the absolute value of the drive current I isrelatively small in the first period and relatively large in the secondperiod.

Incidentally, in the example shown in FIG. 13, the absolute value of thedrive current I in the first period and the absolute value of the drivecurrent I in the second period are constant in each period; however, theinvention is not limited thereto. For example, when the absolute valueof the drive current I in the first period and the absolute value of thedrive current I in the second period vary in each period, the controlsection 40 may control the discharge lamp driving section 230 so thatthe average value of the absolute value of the drive current I in eachperiod becomes relatively small in the first period and relatively largein the second period. Moreover, for example, when the absolute value ofthe drive current I in the first period and the absolute value of thedrive current I in the second period vary in each period, the controlsection 40 may control the discharge lamp driving section 230 so as totake the minimum value of the absolute value of the drive current I inthe first period and take the maximum value of the absolute value of thedrive current I in the second period. In the projector 500 according tothe second embodiment, in the third control, in the first period, thecontrol section 40 may control the discharge lamp driving section 230 sothat the discharge lamp driving section 230 supplies an alternatingcurrent to the discharge lamp 90 as the drive current I. In the exampleshown in FIG. 13, the control section 40 controls the discharge lampdriving section 230 so that the discharge lamp driving section 230generates an alternating current corresponding to one period byreversing the polarity with the absolute value of the current value ofthe drive current I kept constant in the first period and supplies thealternating current to the discharge lamp 90 as the drive current I.Moreover, in the example shown in FIG. 13, an alternating current offour periods is supplied to the discharge lamp 90 as the drive current Iin one first period. The frequency of the alternating current can beexperimentally determined in accordance with the characteristics of thedischarge lamp 90. For example, the frequency of the alternating currentmay be selected in the 30 Hz-to-1 kHz range.

Incidentally, in the projector 500 according to the second embodiment,in the third control, in the first period, the control section 40 maycontrol the discharge lamp driving section 230 so that the dischargelamp driving section 230 supplies a direct current to the discharge lamp90 as the drive current I. In this case, the control section 40 maycontrol the discharge lamp driving section 230 so that, for example, thedischarge lamp driving section 230 supplies, to the discharge lamp 90, adirect current as the drive current I, the direct current having reversepolarity in two first periods which sandwich one second period in termsof time. This makes it possible to keep a heat load balance between theelectrodes of the discharge lamp. As a result, it is possible to preventonly one of the electrodes of the discharge lamp from wearing out.

In the projector 500 according to the second embodiment, the controlsection 40 controls the discharge lamp driving section 230 so that thedischarge lamp driving section 230 supplies, to the discharge lamp 90, adrive current I by which the difference between the energy provided tothe first electrode 92 in the second period and the energy provided tothe second electrode 93 in the second period in the third control issmaller than those in the first control and the second control. That is,the difference between the energy provided to the first electrode 92 inthe second period and the energy provided to the second electrode 93 inthe second period in the third control is smaller than the differencebetween the energy provided to the first electrode 92 in the secondperiod and the energy provided to the second electrode 93 in the secondperiod in the first control and is smaller than the difference betweenthe energy provided to the first electrode 92 in the second period andthe energy provided to the second electrode 93 in the second period inthe second control.

In the example shown in FIG. 13, in the projector 500 according to thesecond embodiment, in the third control, in the second period, thecontrol section 40 controls the discharge lamp driving section 230 sothat the discharge lamp driving section 230 supplies an alternatingcurrent to the discharge lamp 90 as the drive current I. In the exampleshown in FIG. 13, the control section 40 controls the discharge lampdriving section 230 so that the discharge lamp driving section 230generates an alternating current corresponding to one period byreversing the polarity with the absolute value of the current value ofthe drive current I kept constant in the second period and supplies thealternating current to the discharge lamp 90 as the drive current I.Moreover, in the example shown in FIG. 13, the control section 40controls the discharge lamp driving section 230 so that the dischargelamp driving section 230 reverses the polarity of the drive current Iwith such timing that the length of time for which the first polaritycontinues is the same as the length of time for which the secondpolarity continues. In the example shown in FIG. 13, an alternatingcurrent of two periods is supplied to the discharge lamp 90 as the drivecurrent I in one second period.

Incidentally, in the projector 500 according to the second embodiment,in the second period of the third control, the control section 40 maycontrol the discharge lamp driving section 230 so that the dischargelamp driving section 230 reverses the polarity of the drive current Iwith such timing that the length of time for which the first polaritycontinues is different from the length of time for which the secondpolarity continues. In this case, the control section 40 may control thedischarge lamp driving section 230 so that the discharge lamp drivingsection 230 reverses the polarity of the drive current T in such a waythat the difference between the length of time for which the firstpolarity continues and the length of time for which the second polaritycontinues in the second period of the third control becomes smaller thanthe difference between the length of time for which the first polaritycontinues and the length of time for which the second polarity continuesin the first control and the second control. As described above, in thethird control, the control section 40 controls the discharge lampdriving section 230 so that the discharge lamp driving section 230supplies, to the discharge lamp 90, the drive current I that keeps aheat load balance between the electrodes of the discharge lamp 90 as awhole (the drive current I that hardly suffers from a lack of heat loadbalance) as compared to the first control and the second control.

In the projector 500 according to the second embodiment, the controlsection 40 may perform at least one of the first control and the secondcontrol in a period sandwiched between the third control periods whichare next to each other in terms of time. In the example shown in FIG.12, the third control period from time t11 to time t13 and the thirdcontrol period from time t15 to time t17 are next to each other in termsof time. A period from time t13 to time t15, the period sandwichedbetween the two third control periods, is a first control period.Moreover, in the example shown in FIG. 12, the third control period fromtime t15 to time t17 and the third control period from time t19 to timet21 are next to each other in terms of time. A period from time t17 totime t19, the period sandwiched between the two third control periods,is a second control period.

As described above, as a result of the control section 40 performing atleast one of the first control and the second control in a periodsandwiched between the third control periods which are next to eachother in terms of time, it is possible to prevent harmful effects suchas blackening caused by too high fusibility of the electrode due to thefirst control and the second control.

Moreover, as shown in FIG. 12, also in the second embodiment, as in thefirst embodiment, the first control is performed in the first controlperiod and the second control is performed in the second control periodwhich is at least part of the period sandwiched between the firstcontrol periods which are next to each other in terms of time. As aresult, it is possible to keep a heat load balance between the firstelectrode 92 and the second electrode 93 of the discharge lamp 90. Thismakes it possible to prevent only one of the electrodes of the dischargelamp from wearing out.

3. Projector According to Third Embodiment

Next, a projector 500 according to a third embodiment will be described.The configurations of the optical systems and the circuits of theprojector 500 according to the third embodiment are the same as those ofthe projector 500 according to the first embodiment. Therefore, in thefollowing description, a specific example of control of the drivecurrent z in the projector 500 according to the third embodiment will bedescribed. Moreover, the contents of the first control, the secondcontrol, and the third control are the same as those of the firstembodiment and the second embodiment, and therefore a detaileddescription thereof is omitted.

The projector 500 according to the third embodiment includes a statedetecting section (a voltage detecting section 60) that detects adeteriorating state of the discharge lamp 90, and the control section 40shortens the third control period with the progress of the deterioratingstate.

The state detecting section may detect, as a value indicating the degreeof the deteriorating state, for example, the drive voltage Vla of thedischarge lamp 90, a temporal change in the drive voltage Vla of thedischarge lamp 90, the amount of light of the discharge lamp 90, atemporal change in the amount of light of the discharge lamp 90,accumulated lighting time of the discharge lamp 90, or the like. In thethird embodiment, the voltage detecting section 60 (the state detectingsection) detects the drive voltage Vla of the discharge lamp 90 as thedeteriorating state of the discharge lamp 90.

FIG. 14 is a flowchart showing a control example of the projector of thethird embodiment. In the flowchart shown in FIG. 14, the control whichis performed after the discharge lamp 90 is stably turned on until it isturned off is shown. First, the voltage detecting section 60 detects thedrive voltage Vla (step S100). Next, the control section 40 selects adrive condition corresponding to the drive voltage Vla detected in stepS100 from the correspondence stored in the storing section 44 (stepS102).

FIG. 15 is a diagram showing an example of the correspondence betweendrive conditions. In an example shown in FIG. 15, the first controlperiod and the second control period have a constant length and arethree times longer than a period sandwiched between, a time at whichswitching is performed and the next time at which switching isperformed. Moreover, the length of the third control period becomesshorter as the drive voltage Vla becomes greater (as the deterioratingstate of the discharge lamp 90 progresses). In the example shown in FIG.15, the third control period is three times longer than the periodsandwiched between a time at which switching is performed and the nexttime at which switching is performed when the drive voltage Vla is lessthan 80 V, is twice as long as the period sandwiched between a time atwhich switching is performed and the next time at which switching isperformed when the drive voltage Vla is 80 V or more but less than 95 V,and is as long as the period sandwiched between a time at whichswitching is performed and the next time at which switching is performedwhen the drive voltage Vla is 95 V or more.

After the drive condition is selected in step S102 of FIG. 14, thecontrol section 40 determines whether or not there is a need to changethe drive condition (step S104). If the control section 40 determinesthat there is a need to change the drive condition (YES in step S104),the control section 40 changes the drive condition to the drivecondition selected in step S102 and drives the discharge lamp 90 (stepS106). If the control section 40 determines that there is no need tochange the drive condition (NO in step S104), the control section 40continues to drive the discharge lamp 90 in a previous drive condition.

When NO is chosen in step S104 or after step S106 is performed, thecontrol section 40 determines whether or not an instruction to turn offthe discharge lamp 90 is provided (step S108). If the control section 40determines that an instruction to turn off the discharge lamp 90 isprovided (YES in step S108), the control section 40 ends lighting of thedischarge lamp 90 (turns off the discharge lamp 90). If the controlsection 40 determines that an instruction to turn off the discharge lamp90 is not provided (NO in step S108), the control section 40 repeats thecontrol from steps S100 to S108 until an instruction to turn off thedischarge lamp 90 is provided.

When the deteriorating state of the first electrode 92 and the secondelectrode 93 of the discharge lamp 90 progresses, the distance betweenthe first electrode 92 and the second electrode 93 (the distance betweenthe electrodes) is increased. When the distance between the electrodesis increased, the drive voltage via rises. That is, the drive voltageVla rises with the progress of the deteriorating state.

Therefore, in the projector 500 of the third embodiment, the thirdcontrol period is shortened with a rise in the drive voltage Vla (withthe progress of the deteriorating state). When the deteriorating stateof the discharge lamp 90 progresses, the fusibility of the electrode isreduced. Thus, by increasing the frequency of the first control and thesecond control by shortening the third control period with the progressof the deteriorating state of the discharge lamp 90, it is possible toincrease the fusibility of the electrode and prevent deformation of theelectrode. Moreover, when the deteriorating state of the discharge lamp90 does not progress, by not increasing the fusibility of the electrodemore than necessary, it is possible to prevent harmful effects such asblackening caused by too high fusibility of the electrode.

4. Projector According to Fourth Embodiment

Next, a projector 500 according to a fourth embodiment will bedescribed. The configurations of the optical systems and the circuits ofthe projector 500 according to the fourth embodiment are the same asthose of the projector 500 according to the first embodiment. Therefore,in the following description, a specific example of control of the drivecurrent I in the projector 500 according to the fourth embodiment willbe described. Moreover, the contents of the first control, the secondcontrol, and the third control are the same as those of the firstembodiment and the second embodiment, and therefore a detaileddescription thereof is omitted.

The projector 500 according to the fourth embodiment includes a statedetecting section (a voltage detecting section 60) that detects adeteriorating state of the discharge lamp 90. The control section 40lengthens the first control period and the second control period withthe progress of the deteriorating state.

The state detecting section may detect, as a value indicating the degreeof the deteriorating state, for example, the drive voltage Vla of thedischarge lamp 90, a temporal change in the drive voltage Vla of thedischarge lamp 90, the amount of light of the discharge lamp 90, atemporal change in the amount of light of the discharge lamp 90,accumulated lighting time of the discharge lamp 90, or the like. In thefourth embodiment, the voltage detecting section 60 (the state detectingsection) detects the drive voltage Vla of the discharge lamp 90 as thedeteriorating state of the discharge lamp 90.

A control flow in the fourth embodiment is the same as the control flowin the third embodiment described by using FIG. 14, and differstherefrom only in the correspondence between the drive conditionsselected in step S102.

FIG. 16 is a diagram showing an example of the correspondence betweendrive conditions. In an example shown in FIG. 16, the third controlperiod has a constant length and is three times longer than a periodsandwiched between a time at which switching is performed and the nexttime at which switching is performed. Moreover, the lengths of the firstcontrol period and the second control period become longer as the drivevoltage via becomes greater (as the deteriorating state of the dischargelamp 90 progresses). In the example shown in FIG. 16, the first controlperiod and the second control period are as long as the periodsandwiched between a time at which switching is performed and the nexttime at which switching is performed when the drive voltage Vla is lessthan 80 V, are twice as long as the period sandwiched between a time atwhich switching is performed and the next time at which switching isperformed when the drive voltage Vla is 80 V or more but less than 95 V,and are three times longer than the period sandwiched between a time atwhich switching is performed and the next time at which switching isperformed when the drive voltage Vla is 95 V or more.

When the deteriorating state of the first electrode 92 and the secondelectrode 93 of the discharge lamp 90 progresses, the distance betweenthe first electrode 92 and the second electrode 93 (the distance betweenthe electrodes) is increased. When the distance between the electrodesis increased, the drive voltage Vla rises. That is, the drive voltageVla rises with the progress of the deteriorating state.

Therefore, in the projector 500 of the fourth embodiment, the firstcontrol period and the second control period are lengthened with a risein the drive voltage Vla (with the progress of the deteriorating state).When the deteriorating state of the discharge lamp 90 progresses, thefusibility of the electrode is reduced. Thus, by lengthening the firstcontrol period and the second control period with the progress of thedeteriorating state of the discharge lamp 90, it is possible to increasethe fusibility of the electrode and prevent deformation of theelectrode. Moreover, when the deteriorating state of the discharge lamp90 does not progress, by not increasing the fusibility of the electrodemore than necessary, it is possible to prevent harmful effects such asblackening caused by too high fusibility of the electrode. Incidentally,in the third embodiment, an example in which the third control period isshortened as the deteriorating state of the discharge lamp 90 progresseshas been described, and, in the fourth embodiment, an example in whichthe first control period and the second control period are lengthened asthe deteriorating state of the discharge lamp 90 progresses has beendescribed. However, these examples can be combined.

In the embodiments described above, a configuration in which theprojector 500 makes the observer view a display picture stereoscopicallyby using a first picture and a second picture as a picture for the lefteye and a picture for the right eye, respectively, has been adopted;however, the invention is not limited thereto. For example, as aprojector, a configuration in which a first picture and a second pictureare provided as pictures with different contents and different observersare made to identify visually two display pictures (the first pictureand the second picture) in such a way that one observer views one of thedisplay pictures and the other observer views the other of the displaypictures may be adopted.

When such a configuration is adopted, as the active shutter glasses, itis necessary simply to provide two types of glasses: glasses having, onthe right and left eyeglasses, shutters that operate in the same way asthe right shutter 412 described earlier and glasses having, on the rightand left eyeglasses, shutters that operate in the same way as the leftshutter 414 described earlier.

In the embodiments described above, a description has been given bytaking up a projector using three liquid crystal panels as an example;however, the invention is not limited thereto. The invention can also beapplied to a projector using one, two, or four or more liquid crystalpanels.

In the embodiments described above, a description has been given bytaking up a transmissive projector as an example; however, the inventionis not limited thereto. The invention can also be applied to areflective projector. Here, “transmissive” means that, like atransmissive liquid crystal panel or the like, an electroopticmodulating device as a light modulating unit transmits light, and“reflective” means that, like a reflective liquid crystal panel, amicromirror light modulating device, or the like, an electroopticmodulating device as a light modulating unit reflects light. As themicromirror light modulating device, a DMD (Digital Micromirror Device,which is a trademark of Texas Instruments Inc.), for example, can beused. The same effects as those of the transmissive projector can alsobe obtained when the invention is applied to the reflective projector.

The invention can be applied to a front projection projector whichprojects a projection image from the observer's side and a rearprojection projector which projects a projection image from the sideopposite to the observer's side.

It is to be understood that the invention is not limited to theembodiments described above and various modifications are possiblewithin the scope of the subject matter of the invention.

The invention includes a configuration which is substantially identicalto the configuration described in the embodiment (for example, aconfiguration having the same function, method, and result as those ofthe configuration described in the embodiment or a configuration havingthe same objective and effects as those of the configuration describedin the embodiment). Moreover, the invention includes a configuration inwhich a nonessential portion of the configuration described in theembodiment is replaced with another portion. Furthermore, the inventionincludes a configuration that can obtain the same effects as those ofthe configuration described in the embodiment or achieve the sameobjective as that of the configuration described in the embodiment. Inaddition, the invention includes a configuration which is obtained byadding a publicly-known technique to the configuration described in theembodiment. The entire disclosure of Japanese Patent Application No.2010-278936, filed Dec. 15, 2010 is expressly incorporated by referenceherein.

What is claimed is:
 1. A projector that outputs a first picture and asecond picture alternately while performing switching between the firstpicture and the second picture with given switching timing, comprising:a discharge lamp including a first electrode and a second electrode; adischarge lamp driving section that supplies, to the discharge lamp, adrive current that drives the discharge lamp; and a control section thatcontrols the discharge lamp driving section, wherein a switching periodsandwiched between a time at which switching is performed and the nexttime at which switching is performed starts with a first period and endswith a second period, the control section performs a first controlprocessing in a first control period which continues at least for oneswitching period and performs a second control processing in a secondcontrol period which continues at least for one switching period, in thefirst control processing and the second control processing, the controlsection controls the discharge lamp driving section so that the absolutevalue of the drive current becomes relatively small in the first periodand becomes relatively large in the second period, in the first controlprocessing, in the second period, the control section controls thedischarge lamp driving section so that the drive current by which theenergy provided to the first electrode becomes greater than the energyprovided to the second electrode is supplied to the discharge lamp, andin the second control processing, in the second period, the controlsection controls the discharge lamp driving section so that the drivecurrent by which the energy provided to the second electrode becomesgreater than the energy provided to the first electrode is supplied tothe discharge lamp.
 2. The projector according to claim 1, wherein thecontrol section performs the second control processing in at least partof a period sandwiched between the first control periods which are nextto each other in terms of time.
 3. The projector according to claim 1,wherein the control section performs third control processing in a thirdcontrol period which continues at least for one switching period, and inthe third control processing, the control section controls the dischargelamp driving section so that the absolute value of the drive currentbecomes relatively small in the first period and becomes relativelylarge in the second period, the control section controls the dischargelamp driving section so that the drive current by which the differencebetween the energy provided to the first electrode in the second periodand the energy provided to the second electrode in the second period issmaller than the differences in the first control processing and thedifference in the second control processing is supplied to the dischargelamp, and the control section performs at least one of the first controlprocessing and the second control processing in a period sandwichedbetween the third control periods which are next to each other in termsof time.
 4. The projector according to claim 3, further comprising: astate detecting section detecting a deteriorating state of the dischargelamp, wherein the control section shortens the third control period withthe progress of the deteriorating state.
 5. The projector according toclaim 3, further comprising: a state detecting section detecting adeteriorating state of the discharge lamp, wherein the control sectionlengthens the first control period and the second control period withthe progress of the deteriorating state.
 6. The projector according toclaim 1, wherein in the first control processing, the control sectioncontrols the discharge lamp driving section so that a direct current bywhich the first electrode becomes a positive electrode is supplied tothe discharge lamp as the drive current, and in the second controlprocessing, the control section controls the discharge lamp drivingsection so that a direct current by which the second electrode becomes apositive electrode is supplied to the discharge lamp as the drivecurrent.
 7. The projector according to claim 1, wherein in the firstcontrol processing, the control section controls the discharge lampdriving section so that an alternating current by which the time inwhich the first electrode is a positive electrode is longer than thetime in which the second electrode is a positive electrode in one periodis supplied to the discharge lamp as the drive current, and in thesecond control processing, the control section controls the dischargelamp driving section so that an alternating current by which the time inwhich the second electrode is a positive electrode is longer than thetime in which the first electrode is a positive electrode in one periodis supplied to the discharge lamp as the drive current.
 8. The projectoraccording to claim 1, wherein in the first control processing, thecontrol section controls the discharge lamp driving section so as toinclude a period in which an alternating current is supplied to thedischarge lamp as the drive current and a period in which a directcurrent by which the first electrode becomes a positive electrode issupplied to the discharge lamp as the drive current, and in the secondcontrol processing, the control section controls the discharge lampdriving section so as to include a period in which an alternatingcurrent is supplied to the discharge lamp as the drive current and aperiod in which a direct current by which the second electrode becomes apositive electrode is supplied to the discharge lamp as the drivecurrent.
 9. A projection system comprising; the projector according toclaim 1, and a shutter glasses including a first shutter and a secondshutter, wherein the first shutter and the second shutter are switchedbetween an open state and a closed state based on a signal from thecontrol section, when the first picture is output, in the first period,both of the first shutter and the second shutter are in the closedstate, and in the second period, the first shutter is the open state andthe second shutter is closed state, and when the second picture isoutput, in the first period, both of the first shutter and the secondshutter are in the closed state, and in the second period, the secondshutter is the open state and the first shutter is closed state.